Sclerotinia sclerotiorum, causal agent of white mould, is the most destructive and widely distributed soilborne pathogen of common bean during the autumn–winter season in Brazil. Nevertheless, little is known about the genetic structure of the pathogen population. Microsatellite (SSR) markers and mycelial compatibility groups (MCGs) were used to characterize 118 isolates collected from 20 bean fields located in the most important growing regions of Minas Gerais State (MG). Additionally, the genetic variability among 10 isolates obtained from a single sclerotium was investigated in 10 different sclerotia. Seventy SSR haplotypes and 14 MCGs were identified among the 118 isolates. The genetic differences within bean growing areas accounted for most of the genetic variation (72%). Despite the relatively high genotypic diversity, the SSR loci were at linkage disequilibrium. Moreover, 70% of the isolates were assigned to only two MCGs, and haplotypes of a given MCG were closely related. The discriminant analysis of principal components revealed five groups. There was strong genetic differentiation between isolates collected in one municipality in southern MG when compared to other regions. Common bean resistance to white mould should be assessed with representative isolates of the five genetic groups and, if possible, of the different MCGs detected in the present study. One to five haplotypes were detected among the 10 isolates obtained from a single sclerotium. Therefore, in order to ensure genetic identity of an isolate, hyphal tip or monoascosporic isolates should be used.

Diseases caused by begomoviruses are a serious constraint to crop production in many tropical and subtropical areas of the world, including Brazil. Begomoviruses are whitefly-transmitted, single-stranded DNA viruses that are often associated with weed plants, which may act as natural reservoirs of viruses that cause epidemics in crop plants. Cleome affinis (family Capparaceae) is an annual weed that is frequently associated with leguminous crops in Brazil. Samples of C. affinis were collected in four states in the northeast of Brazil. Analysis of 14 full-length DNA-A components revealed that only one begomovirus was present, with 91-96% identity to cleome leaf crumple virus (ClLCrV). In a phylogenetic tree, ClLCrV forms a basal group relative to all other Brazilian begomoviruses. Evidence of multiple recombination events was detected among the ClLCrV isolates, which also display a high degree of genetic variability. Despite ClLCrV being the only begomovirus found, its phylogenetic placement, high genetic variability and recombinant nature suggest that C. affinis may act as a source of novel viruses for crop plants. Alternatively, ClLCrV could be a genetically isolated begomovirus. Further studies on the biological properties of ClLCrV should help to clarify the role of C. affinis in the epidemiological scenario of Brazilian begomoviruses.

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